neuroanatomy Neuroanatomy is the study of the structure and organization of the nervous system. In contrast to animals with radial symmetry, whose nervous system consists of a distributed network of cells, animals with bilateral symmetry have segregated, defi ...

, a sulcus (

Latin Latin ( or ) is a classical language belonging to the Italic languages, Italic branch of the Indo-European languages. Latin was originally spoken by the Latins (Italic tribe), Latins in Latium (now known as Lazio), the lower Tiber area aroun ...

: "furrow"; : sulci) is a shallow depression or groove in the

cerebral cortex The cerebral cortex, also known as the cerebral mantle, is the outer layer of neural tissue of the cerebrum of the brain in humans and other mammals. It is the largest site of Neuron, neural integration in the central nervous system, and plays ...

. One or more sulci surround a

gyrus In neuroanatomy, a gyrus (: gyri) is a ridge on the cerebral cortex. It is generally surrounded by one or more sulci (depressions or furrows; : sulcus). Gyri and sulci create the folded appearance of the brain in humans and other mammals. ...

(pl. gyri), a ridge on the surface of the cortex, creating the characteristic folded appearance of the

brain The brain is an organ (biology), organ that serves as the center of the nervous system in all vertebrate and most invertebrate animals. It consists of nervous tissue and is typically located in the head (cephalization), usually near organs for ...

human Humans (''Homo sapiens'') or modern humans are the most common and widespread species of primate, and the last surviving species of the genus ''Homo''. They are Hominidae, great apes characterized by their Prehistory of nakedness and clothing ...

s and most other

mammal A mammal () is a vertebrate animal of the Class (biology), class Mammalia (). Mammals are characterised by the presence of milk-producing mammary glands for feeding their young, a broad neocortex region of the brain, fur or hair, and three ...

s. The larger sulci are also called fissures. The cortex develops in the

fetal A fetus or foetus (; : fetuses, foetuses, rarely feti or foeti) is the unborn offspring of a viviparous animal that develops from an embryo. Following the embryonic stage, the fetal stage of development takes place. Prenatal development is a ...

stage of corticogenesis, preceding the cortical folding stage known as

gyrification Gyrification is the process of forming the characteristic folds of the cerebral cortex. The peak of such a fold is called a ''gyrus'' (pl. ''gyri''), and its trough is called a ''Sulcus (neuroanatomy), sulcus'' (pl. ''sulci''). The neurons of the ...

. The large fissures and main sulci are the first to develop. Mammals that have a folded cortex are known as ''gyrencephalic'', and the small-brained mammals that have a smooth cortex, such as

rat Rats are various medium-sized, long-tailed rodents. Species of rats are found throughout the order Rodentia, but stereotypical rats are found in the genus ''Rattus''. Other rat genera include '' Neotoma'' (pack rats), '' Bandicota'' (bandicoo ...

s and

mice A mouse (: mice) is a small rodent. Characteristically, mice are known to have a pointed snout, small rounded ears, a body-length scaly tail, and a high breeding rate. The best known mouse species is the common house mouse (''Mus musculus' ...

are termed lissencephalic.

Structure

Sulci, the grooves, and gyri, the folds or ridges, make up the folded surface of the

. Larger or deeper sulci are also often termed fissures. The folded cortex creates a larger surface area for the brain in humans and other larger mammals, without the need of increasing the size of the

skull The skull, or cranium, is typically a bony enclosure around the brain of a vertebrate. In some fish, and amphibians, the skull is of cartilage. The skull is at the head end of the vertebrate. In the human, the skull comprises two prominent ...

. In the

human brain The human brain is the central organ (anatomy), organ of the nervous system, and with the spinal cord, comprises the central nervous system. It consists of the cerebrum, the brainstem and the cerebellum. The brain controls most of the activi ...

, two-thirds of the folded cortex is buried within the sulci, if the division of the hemispheres by the longitudinal fissure is taken into account. The sulci and fissures are shallow and deep grooves respectively in the cortex, that organise the brain into its regions. A sulcus is a shallow groove that surrounds a gyrus or part of a gyrus. A fissure is a deeper furrow that divides the brain into lobes, and also into the two hemispheres as the longitudinal fissure. Fissures are the most prominent and invariable of the sulci. The

pia mater Pia mater ( or ),Entry "pia mater"
in
arachnoid mater stretches across all sizes of the sulci, except the longitudinal fissure where it follows the pia mater. Consequently the inner sides of almost all sulci are separated only by the pia mater and the subarachnoid space, in which the

cerebrospinal fluid Cerebrospinal fluid (CSF) is a clear, colorless Extracellular fluid#Transcellular fluid, transcellular body fluid found within the meninges, meningeal tissue that surrounds the vertebrate brain and spinal cord, and in the ventricular system, ven ...

circulates. Sulci may be considered as extensions of the subarachnoid space. The approximate depth of a sulcus ranges between one and three centimetres. Other parameters of sulcal shape are length, width, and surface area. Within a sulcus there may be smaller gyri, collectively known as ''transverse gyri''. A sulcus is not necessarily a single structure. Some sulci have one or more parts that may branch in different directions. Such parts may be short, long, isolated, or connected to other sulci.

Variations

The sulcal pattern varies between human individuals, but the sulci and gyri do have a generalised arrangement, making a common nomenclature possible.

Types

On the basis of formation: #Large primary sulci: formed before birth, independently, such as the precentral sulcus and the

central sulcus In neuroanatomy, the central sulcus (also central fissure, fissure of Rolando, or Rolandic fissure, after Luigi Rolando) is a sulcus, or groove, in the cerebral cortex in the brains of vertebrates. It is sometimes confused with the longitudinal ...

. #Short primary sulci include rhinal sulcus, olfactory sulcus, occipital sulcus, and

lateral sulcus The lateral sulcus (or lateral fissure, also called Sylvian fissure, after Franciscus Sylvius) is the most prominent sulcus (neuroanatomy), sulcus of each cerebral hemisphere in the human brain. The lateral sulcus (neuroanatomy), sulcus is a deep ...

. #Short branched sulci sulci with several branches such as the subparietal sulcus, and orbital sulcus. #Short free supplementary sulci include the lunate sulcus, and medial frontal sulcus. #Sulci with side branches that connect adjacent parallel sulci. On the basis of function: #A limiting sulcus separates at its floor into two areas which are different functionally and structurally e.g. central sulcus between the motor and sensory areas. #Axial sulcus develops in the long axis of a rapidly growing homogeneous area e.g. postcalcarine sulcus in the long axis of the striate area. #Operculated sulcus separates by its lips into two areas and contains a third area in the walls of the sulcus e.g. lunate sulcus is an operculated sulcus, separating the striate and parastriate areas. On the basis of depth: #Complete sulcus is very deep so as to cause elevation in the walls of the lateral ventricle. Examples are the collateral and calcarine sulci. #Incomplete sulci are superficially situated and are not very deep, E.g. paracentral sulcus. Early gyrification

Development

The process of cortical folding is complex and incompletely understood. It is explained by a number of hypotheses including mechanical buckling, and axonal tension factors. The hypotheses are not mutually exclusive and can include their combined effects, with that of another mechanism of tangential expansion. Tangential expansion is associated with radial glial cells, and a process of intercalation of cortical neurons in between cells of the outer cortical plate layer producing the outward buckling of a gyrus. In humans, cerebral convolutions appear at about five months and take at least into the first year after birth to fully develop. There is a hierarchy of morphological development with the fissures and main sulci developing ahead of others. The first sulci to develop are the primary sulci, followed by secondary sulci. The more constantly found sulci are those related to functional specialization. Tertiary sulci develop primarily after birth. The development of the tertiary sulci seems to be unaffected by genetics, and more related to environmental factors. Development varies greatly between individuals. The potential influences of genetic,

epigenetic In biology, epigenetics is the study of changes in gene expression that happen without changes to the DNA sequence. The Greek prefix ''epi-'' (ἐπι- "over, outside of, around") in ''epigenetics'' implies features that are "on top of" or "in ...

and environmental factors are not fully understood.

Sulci of note

; Frontal lobe Superior frontal sulcus, Inferior frontal sulcus, Precentral sulcus, Olfactory sulcus, Orbital sulcus, Paracentral sulcus ; Parietal lobe Intraparietal sulcus, Marginal sulcus, Postcentral sulcus ; Occipital lobe Lunate sulcus, Transverse occipital sulcus, Calcarine sulcus ; Temporal lobe

Superior temporal sulcus The superior temporal sulcus (STS) is the sulcus separating the superior temporal gyrus from the middle temporal gyrus, in the temporal lobe of the mammalian brain. A sulcus (plural sulci) is a deep groove that curves into the largest part of ...

, Inferior temporal sulcus ; Interlobar fissures Longitudinal fissure,

Central sulcus In neuroanatomy, the central sulcus (also central fissure, fissure of Rolando, or Rolandic fissure, after Luigi Rolando) is a sulcus, or groove, in the cerebral cortex in the brains of vertebrates. It is sometimes confused with the longitudinal ...

Lateral sulcus The lateral sulcus (or lateral fissure, also called Sylvian fissure, after Franciscus Sylvius) is the most prominent sulcus (neuroanatomy), sulcus of each cerebral hemisphere in the human brain. The lateral sulcus (neuroanatomy), sulcus is a deep ...

, Collateral sulcus, Callosal sulcus, Parieto-occipital sulcus, Occipitotemporal sulcus, Subparietal sulcus, Cingulate sulcus ; Limbic lobe Hippocampal sulcus, Rhinal sulcus, Fimbriodentate sulcus, Central sulcus of the insula, Circular sulcus of insula

Clinical significance

The advanced cognitive abilities that have developed from the expansion of cortical folding, are shown to be adversely affected when the folds are malformed. Malformations of the cortical folds have been linked to the intellectual disabilities associated with

epilepsy Epilepsy is a group of Non-communicable disease, non-communicable Neurological disorder, neurological disorders characterized by a tendency for recurrent, unprovoked Seizure, seizures. A seizure is a sudden burst of abnormal electrical activit ...

schizophrenia Schizophrenia () is a mental disorder characterized variously by hallucinations (typically, Auditory hallucination#Schizophrenia, hearing voices), delusions, thought disorder, disorganized thinking and behavior, and Reduced affect display, f ...

, and

autism Autism, also known as autism spectrum disorder (ASD), is a neurodevelopmental disorder characterized by differences or difficulties in social communication and interaction, a preference for predictability and routine, sensory processing d ...

. Anomalies in gyrification can affect the width or depth of sulci that are associated with many neurological or neuropsychiatric disorders. The widening of sulci is seen to indicate early atrophy in

neurodegenerative disorder A neurodegenerative disease is caused by the progressive loss of neurons, in the process known as neurodegeneration. Neuronal damage may also ultimately result in their death. Neurodegenerative diseases include amyotrophic lateral sclerosis, mul ...

s, and may be used as a biomarker in their progression. It has been found that the width of cortical sulci increases not only with age, but also with cognitive decline in the elderly. Ulegyria, is a condition of scarring in the deep regions of sulci leading to disruption of the associated gyri. The sulci are valuable landmarks in microneurosurgery, and may also be used as corridors for

surgeries Surgery is a medical specialty that uses manual and instrumental techniques to diagnose or treat pathological conditions (e.g., trauma, disease, injury, malignancy), to alter bodily functions (e.g., malabsorption created by bariatric surgery ...

Other animals

The variation in the number of fissures in the brain (

) between species is related to the size of the animal and the size of the brain. Mammals that have smooth-surfaced or nonconvoluted brains are called lissencephalics and those that have folded or convoluted brains gyrencephalics. The division between the two groups occurs when cortical surface area is about 10 cm² and the brain has a volume of 3–4 cm³. Large rodents such as beavers () and capybaras () are gyrencephalic, and smaller rodents such as rats and mice, and some

New World monkey New World monkeys are the five families of primates that are found in the tropical regions of Mexico, Central and South America: Callitrichidae, Cebidae, Aotidae, Pitheciidae, and Atelidae. The five families are ranked together as the Ceboi ...

s are lissencephalic.

Macaque

macaque The macaques () constitute a genus (''Macaca'') of gregarious Old World monkeys of the subfamily Cercopithecinae. The 23 species of macaques inhabit ranges throughout Asia, North Africa, and Europe (in Gibraltar). Macaques are principally f ...

has a more simple sulcal pattern. In a monograph Bonin and Bailey list the following as the primary sulci:Gerhardt von Bonin, Percival Bailey, ''The Neocortex of Macaca Mulatta'', The University of Illinois Press, Urbana, Illinois, 1947 * Calcarine fissure (ca) *

(ce) * Sulcus cinguli (ci) * Hippocampal fissure (h) * Sulcus intraparitalis (ip) * Lateral fissure (or Sylvian fissure) (la) * Sulcus olfactorius (olf) * Medial parieto-occipital fissure (pom) * Fissura rhinalis (rh) * Sulcus temporalis superior (ts) – This sulcus runs parallel to the lateral fissure and extends to the temporal pole and often superficially merges with it.

Additional images

File:Sulci of the brain.jpg, upright=1.2, Different views of the sulci of the brain File:Gray726.png, Gray's Fig. 726 – Lateral surface of left cerebral hemisphere, viewed from the left side File:Gray727.svg, Gray's Fig. 727 – Medial surface of left cerebral hemisphere, viewed from the right side

References

External links

Visual explanation of gyri, sulci, and fissures
{{DEFAULTSORT:Sulcus (Neuroanatomy) Neuroanatomy *